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Comment by Alex3917 | Hacker News Reader

I've been trying to break this habit and get into using namedtuples, but the problem is I still need to look up the API every time I need to use them.

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Be careful with named tuples:

    >>> from collections import namedtuple
    >>> Time = namedtuple('Time', ['hours', 'minutes'])
    >>> Point = namedtuple('Point', ['x', 'y'])
    >>> t = Time(hours=7, minutes=40)
    >>> p = Point(x=7, y=40)
    >>> p == t
    True

They're still tuples. They're meant more as a tool for making an already existing tuple mess slightly more managable rather than creating a new mess.

For making plain data objects take less boilerplate to create have a look at attrs: https://attrs.readthedocs.io

Strong +1 for attrs. It is a really nice library and quite easy to use.

Interesting find with attrs. My main use case for namedtuples is a class as a data container which doesn't require any special methods. This might be a better alternative.

Ugh, that's terrible... Thanks for pointing it out!

When something is moderately awkward I often make a "snippet" in my editor, e.g.:

    pr<TAB> -->  print('%cursor%', %cursor%)
    nt<TAB> -->  namedtuple('%cursor%', ['%cursor%', …])

Classes work for this as well, I've found.

I use a lot of classes.

It feels like Java sometimes, but it does make debugging easier...

In my experience, namedtuples have significantly less overhead than classes.

Yes for the increased overhead, but I find that the fact that they're tuples underneath results in odd semantics (I think the comment above mine[1] does a decent job pointing out why I am leary of using them.

Tradeoffs, I guess.

[1] https://news.ycombinator.com/item?id=13124501

I doubt that because defining a namedtuple just creates a new class internally: https://github.com/python/cpython/blob/master/Lib/collection...

Class creation the very expensive in Python, so Guido van Rossum explicitly recommends against using dynamically created namedtuples: https://mail.python.org/pipermail//python-ideas/2016-April/0...

I believe that objects of namedtuple have less runtime overhead than a class. Guido seems to point out that the process of instantiating a namedtuple class is expensive.

Normally, yes. But if you define __slots__ on the class, it's the same overhead as a namedtuple (no __dict__ per instance).

Besides immutability, what are the advantages of using namedtuples instead of dicts?

- A clear single point of truth describing your data.

- Probably more memory efficient.

We can test memory usage in CPython (3.5)!

  >>> import collections
  >>> import sys
  >>> class A:
  ...     def __init__(self, x, y):
  ...         self.x = x
  ...         self.y = y
  ... 
  >>> class B:
  ...     __slots__ = ('x', 'y')
  ...     def __init__(self, x, y):
  ...         self.x = x
  ...         self.y = y
  ... 
  >>> C = collections.namedtuple('C', ('x', 'y'))
  >>> a = A(1, 1)
  >>> b = B(1, 1)
  >>> c = C(1, 1)
  >>> d = {'x': 1, 'y': 1}
  >>> sys.getsizeof(a) + sys.getsizeof(a.__dict__) # Plain object
  344
  >>> sys.getsizeof(b) + sys.getsizeof(b.__slots__) # Plain object with slots
  120
  >>> sys.getsizeof(c) # Named Tuple
  64
  >>> sys.getsizeof(d) # Dict
  288

EDIT: Fixed a slew of measurement issues

EDIT2: Included size of __slots__ tuple

If you're using Python 3.5, use tracemalloc, it is much nicer for this sort of thing.

https://docs.python.org/3/library/tracemalloc.html

It is an order of magnitude slower and not less memory efficient. Also, for me it is never easier to understand what is going on when named tuples are used instead of dicts

Proof:

    def make_dicts():
        res = []
        for i in range(1000000):
            res.append({'x': i, 'y': i})
        return res

    def make_tuples():
        templ = namedtuple('Point', ('x', 'y'))
        res = []
        for i in range(1000000):
            res.append(templ(i, i))
        return res

    from ipython_memory_usage import ipython_memory_usage as imu
    imu.start_watching_memory()
    used 0.2305 MiB RAM in 4.00s, peaked 0.00 MiB above current, total RAM usage 86.41 MiB

    %time tuples = make_tuples()
    CPU times: user 780 ms, sys: 32 ms, total: 812 ms
    Wall time: 816 ms
    used 109.0625 MiB RAM in 0.92s, peaked 0.00 MiB above current, total RAM usage 195.47 MiB

    %time dicts = make_dicts()
    CPU times: user 160 ms, sys: 32 ms, total: 192 ms
    Wall time: 194 ms
    used 99.5117 MiB RAM in 0.30s, peaked 0.00 MiB above current, total RAM usage 524.33 MiB

Your sibling got opposite results. I haven't dissected either program, but I don't see any obvious flaws. I find your results particularly surprising. Can you explain them? Are there optimisations going on in your benchmark that you haven't accounted for?

It should not be controversial that namedtuples are clearer for the reason I stated in my initial comment.

sys.getsizeof() on a code object returns the size of the code struct, not all the other objects it references.

To measure real usage, you have to use another method. I use ipython_memory_usage because it's easy to use.

You can test this out easily by making a large dict and see how much your OS thinks python is using vs what sys.getsizeof is reporting.

- Dot syntax: foo.length rather than foo['length']

I gives a name and expected properties to common data structures, or unspoken unnamed types.

Many times when a dict is used, it's expected to have certain attributes, and may have expected ways of interacting with those attributes. Named tuples is a simple way to formalize these, which makes them not so mysterious to you future-you, or to other developers who inherit the project 6 months down the road.

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